This invention relates to a clamping apparatus fixed to the top surface of a bed of a machine tool for clamping a workpiece and, in particular, a clamping apparatus for visually displaying the clamping state of the workpiece.
A conventional clamping apparatus for use in clamping a workpiece over the bed of a machine tool has a base block having an upwardly inclined guide surface and fixed to the top surface of the bed and a pressing member having an inclined slide surface. The pressing member slidably contacts the guide surface of the base block at its slide surface and is movable in the vertical direction relative to the top surface of the bed with its horizontal movement relative to the top surface of the bed. The pressing member has a bolt insertion hole extending in the vertical direction and into which a pressing bolt is inserted. The belt insertion hole also extends in said horizontal direction. The forward end of said pressing bolt inserted into the bolt insertion hole is threadably inserted into the base block. When the pressing bolt is rotated in one direction, it is lowered to move the pressing member downwardly over the guide surface of the base block, while at the same also moving it in a horizontal direction.
With a stopper fixed on the top surface of the bed and one side surface of a workpiece abutted against that stopper, the end face of the pressing member which is moved in said one horizontal direction is abutted against the other side surface of the workpiece at a location oppositely facing the stopper, causing the workpiece to be sandwiched by the pressing member and the stopper to clamp the workpiece between the pressing member and the stopper over the top surface of the bed.
In the aforementioned conventional clamping apparatus, the magnitude of a clamping force loaded on the workpiece can be determined only by the clamping torque magnitude of the pressing bolt which is increased substantially in proportion to an increase in the abutting pressure of the pressing member against the other side surface of the workpiece. If the abutting pressure is too smaller than a predetermined proper value, no adequate clamping of the workpiece will be obtained over the top surface of the bed. If, on the other hand, the aforementioned abutting pressure is greater than the aforementioned proper value, then there is a possibility that the workpiece will be warped or that the threads of the pressing bolt will be broken out. In order to prevent the breakage of the threads of pressing bolts and to machine the workpiece on a conventional clamping apparatus with relatively high accuracy, it is required that the abutting pressure of the pressing member against the workpiece on the clamping apparatus be set at the predetermined proper value at all times. To this end, use has been made of a torque wrench.
Where, even in this case, the workpiece is clamped by a plurality of clamping apparatuses, it is done at once with respect to the plurality of clamping apparatuses through the use of a torque wrench and then it is necessary to ascertain, whether or not the clamping forces of the plural clamping apparatuses are constant, again through the use of a torque wrench.